I realized by read the earlier post that when putting batteries in series (like li-fe) the voltage doesn't exactly add up like if each sell is 3.6v add them together it wouldn't give me 7.2v. Why?

I found on eBay a 12pcs 18650 Li-ion batteries rated at 5000mah. I'm looking to replace a 6c 5000mah lipo ( which is 22.2v) I'm think that I only need 5-6 and run them in series which would equal 4.2x5=21. Am I correct?

BShady wrote:I realized by read the earlier post that when putting batteries in series (like li-fe) the voltage doesn't exactly add up like if each sell is 3.6v add them together it wouldn't give me 7.2v. Why?

It does add just like you'd expect. If you don't get the total voltage you expect after seriesing them then you have a problem somewhere.

I found on eBay a 12pcs 18650 Li-ion batteries rated at 5000mah. I'm looking to replace a 6c 5000mah lipo ( which is 22.2v) I'm think that I only need 5-6 and run them in series which would equal 4.2x5=21. Am I correct?

If they're 18650 then I seriously doubt they are anywhere near that capacity. Most likely the seller is making up the specs. There's a lot of threads about various types of 18650, you cna find out from the seller which manufacturer and part number they are, and probably find a thread here or elsewhere about them. If they can't tell you who made them and what model number they are, you can't verify anything about them without buying osme and testng them yourself, and probably shouldn't buy them.

I think you will want to read a lot more threads about various types of batteries before you decide what to buy to replace your existing pack, because it sounds like you still have a fair bit to learn. It's jsut about all here posted already, but will take searching adn reading to find and learn it.

One side qu: what's the difference between mAh and Ah?

It's just SI units, which are documented a number of places, including Wikipedia.

Ypedal wrote:This guids is being written and saved as i go, so bear with me...
Batteries !!..

Lithium, the latest and greatest, alot to cover here, so pls take the time to read it over a few times if it's not clear at first.. You will find terms like " Lipo" and " Li-Ion " and " LiFePo4 " etc.. all lithium batteries are basically Lithium Ion.. but there are many different chemistries available.

example :

Lithium Manganese ( LiMn )
Lithium Cobalt ( LiCo )
Lithium Iron Phosphate ( LiFePo4 )
Lithium Titanate
And more mixes and blends etc.. the most common for ebikes right now are LiMn, LiCo and LiFePo4 so i'll concentrate on those.

LiMn and LiCo both have the same voltage profile, fully charged at 4.20v and fully discharged at 3.0v per cell

LiFePo4 is different, it is fully charged at 3.6v and fully discharged at 2.0v

In order to make a 36v pack from LiMn/LiCo you need 10 cells in series

In order to make a 36v pack from LiFePo4 you need 12 cells in series, because of the lower voltage per cell.

It says that for LiFePo4, which have a cell voltage of 3.6, if you want to make a 36v pack you need 12cells but 12 x 3.6 = 43.2?
That's what I'm not sure about?

And I found on eBay 5300mah Li-ion battery made by GTL
And a 4000mah battery made by ultrafire